The present invention relates to occupant classification systems (OCS) for vehicles. Occupant classification systems are used in vehicles to determine what type of occupant (e.g., adult, child, or infant) is present in the vehicle.
When a vehicle seat is wet, a loading current out of the sensing electrode increases. When a rear facing infant seat (RFIS) contains an infant during a wet seat situation (RFIS/wet), the current out to the electrode may be higher than an adult occupant situation. With a system that only measures the current amplitude out to the sensing electrode, there may be a problematic overlap between the child seat cases and the adult cases.
Some conventional systems, a seat pan and seat back frame may be grounded because of a connection through seat tracks and a seat back angle adjuster to the floor pan. However, these grounding systems can be unreliable.
In vehicles with heated seats, occupant classification systems that are packaged in the vehicle seat above the seat foam must work in close proximity to a seat heater. When occupant classification systems use capacitive sensing or electric field sensing, a seat heater can have a significant affect on the measurements of the OCS. Some conventional systems require that the heater “float” when capacitive sensing measurements are being obtained. In this context, floating means that the heater element has a high impedance to ground. Because the impedance being measured is capacitive in nature, even a small capacitive coupling (>several pF) between the heating element and ground can have an important impact on the capacitive sensing measurements.
In general, it is difficult to “float” the heater consistently. If the heater element is not floating, the mechanical orientation between the sensing element and the heating element can significantly affect the overall response of the system. For example, over the life of a vehicle, the orientation between the heater and capacitive sensor may change. The change in orientation between a heater element and the capacitive sensing element will also affect the performance of an occupant classification system.
In other conventional systems, separate mats for the heater and sensor element are used. Disadvantages to this configuration include the inconvenience of an additional installation process, having additional insulation between the heater and the seat surface, having an extra layer (possibly a shielding layer) between the sensor and the seat surface and having numerous other sources of system interaction.
In another known occupant classification system, the seat heater element also functions as the sensor element. In this system the sensing and heating operations are time multiplexed. The sensor takes about 10% of the available time to make measurements and the remaining 90% of the operational time is used to heat the seat. A drawback to this system is that the sensing electrode is significantly influenced by the heating control electronics. In addition, there is no physical barrier or separation between the heating and sensing ECU.